ARCA

[butters]

They could make the first stage a bit smaller if they just used decomposed HTP. That seems to be a lot less complex, and gets higher Isp, about 117 seconds.

http://www.astronautix.com/h/h2o2.html

I'm sure there's a way to reach orbit of Kerbin given enough RD-107 gas generators.

Also, I'd like to recognize that ARCA is totally crushing the competition for International Astronautical Federation's annual Best Dressed award.

[launchwatcher]

Also, I'd like to recognize that ARCA is totally crushing the competition for International Astronautical Federation's annual Best Dressed award.

Seriously?   Gwynne has him beat by a mile.

[Lars-J]

LOL. I just wasted 45 mins watching that. It's amazing that anyone takes them seriously - but some in this thread have a bizarre need to seem to lend them even fleeting credibility. I don't understand this at all.

Misc thoughts while watching:
- A water rocket is new technology? Since when? (as if the propellant itself has much to do with propulsion technology)
- A lot of attempted dunking on Rocketlab and SpaceX 
- "EcoRocket will fly by next June" - No it won't. It will never fly.
- The mere fact that they are sticking with "sexy" aerospike on BOTH stages should tell you everything you need to know about these charlatans (it makes no sense)
- First he claims that reuse savings have not materialized, until he disagrees with himself later when pimping his rocket as the only competitor to... (next point)
- EcoRocket Heavy is Europe's only chance to compete with SS/SH!!!! 
- Please fund us, we're selling Brooklyn bridges!
- "A European rocket exec called us liars, but that's because they are working on a competing reusable system", and they have polluting SRB's, look at how poisonous they look!!!!!!! (never mind that 1) their reusable rocket is Methalox not solid, and 2) the footage they showed is from an SRB test in Utah)

[xyv]

The video shows a LAS-25D engine test with the small round tank, which is new I believe. They have renamed their small launch vehicle from LAS-25D/HAAS to EcoRocket.

First stage uses technology that is "a very well guarded secret at ARCA" to boost Isp from 50 to 80 seconds. Perhaps they are adding in some hydrogen peroxide to the water to give it a bit more kick, along with carrying batteries to heat the water during flight (which they've mentioned before). Using stainless steel for the rocket would also allow higher temperatures. First stage lands back at the flat launch pad.

Second stage is kerosene and hydrogen peroxide (HTP) using a plug nozzle engine. Propellant mass is 480 kg (70 kg kerosene and 410 kg HTP). From the press conference, dry mass is 40 kg.

Will take off and land on its own legs as exhaust temperature is only 90 C. Schedule is

9 December 2020. Mission 9. Vertical takeoff and landing sequence for first stage.
1 March 2021. Complete ground tests for the second stage.
1 April 2021. Suborbital flight of second stage.
1 June 2021. First orbital launch attempt.
1 October 2021. First qualification flight for commercial services.

€1M development cost. $390K per launch or $39K/kg, which is still very expensive.

"...renamed.. from LAS-25D/HAAS to EcoRocket" - well who is going to fund the former...you need the VC friendly 'ECO' name.  Serious thanks to Steven for having the intestinal fortitude to go through that and log key points.  I mean, 5 - 10 minute "flight of the aerospike" videos are entertaining but no way do I want to spend the better part of an hour trying to glean the nice summary Steven posted.  So:

Vertical takeoff and landing - 9 Dec.  Can't wait and not even a month away...

Suborbital flight of second stage - 1 Apr.  Elon time compressed.  Hmmm...this sounds like a familiar test sequence.  Ignoring the date for now

First orbital launch.  Wow!!  2021 Is going to be such a year for new small launch vehicles.

My favorite wannabee rocket company is back in force.  Please more digestible videos.

[Steven Pietrobon]

Even recent trades have suggested that an aerospike just isn't worth it for a vacuum engine, and with a large-diameter first stage fairing, they could use as big a nozzle as is mass-efficient.

The reason they are using an aerospike on the second stage is for simplicity in attitude control. They just vary the thrust in opposite chambers for pitch and yaw control and use small side motors for roll control. They also changed from linear to circular aerospike as the latter was more mass efficient.

[Lars-J]

Even recent trades have suggested that an aerospike just isn't worth it for a vacuum engine, and with a large-diameter first stage fairing, they could use as big a nozzle as is mass-efficient.

The reason they are using an aerospike on the second stage is for simplicity in attitude control. They just vary the thrust in opposite chambers for pitch and yaw control and use small side motors for roll control. They also changed from linear to circular aerospike as the latter was more mass efficient.

There’s absolutely nothing simple about attitude control with an aerospike. What in the world gives you that impression? Varying the thrust in many small chambers with fine control is not easier than gimbaling a single engine. And mass efficiency and aerospike does not go in the same sentence, be it linear or annular.

[edzieba]

LOL. I just wasted 45 mins watching that. It's amazing that anyone takes them seriously - but some in this thread have a bizarre need to seem to lend them even fleeting credibility. I don't understand this at all.

I don't think anyone gives Arca any credibility, they're a joke at best. But the phase-transition rocket engine is an interesting enough idea on its own that people stick around.

- A water rocket is new technology? Since when? (as if the propellant itself has much to do with propulsion technology)

Not a water rocket like the standard bottle-rocket, where a stored pressurised gas is used to eject a fluid reaction mass. It's a supercritical boiler, basically a controlled BLEVE pointing downwards. It runs from the energy of heating the working fluid that is provided on the ground, plus a small additional amount of energy stored onboard (in a battery, but could just as well be a chemical heat generator) to provide the last bit of energy needed to complete the phase transition. The phase transition allows more reaction mass to be carried in a given tank volume than carrying the reaction mass as a pressurised gas.

[Steven Pietrobon]

There’s absolutely nothing simple about attitude control with an aerospike. What in the world gives you that impression?

Their recent engine tests were for testing this control system, but they have not gone beyond tied down tethered tests so far. Basically its four valves to the four corners of the aerospike, plus valves to the four roll control jets. ARCA believe its a simpler system and have said its the reason why they are using an aerospike on the second stage. From watching their videos, it does look less complex since you don't need a gimbal that can take the thrust of the engine, high force actuators and propellant lines that need to flex.

[Lars-J]

There’s absolutely nothing simple about attitude control with an aerospike. What in the world gives you that impression?

Their recent engine tests were for testing this control system, but they have not gone beyond tied down tethered tests so far. Basically its four valves to the four corners of the aerospike, plus valves to the four roll control jets. ARCA believe its a simpler system and have said its the reason why they are using an aerospike on the second stage. From watching their videos, it does look less complex since you don't need a gimbal that can take the thrust of the engine, high force actuators and propellant lines that need to flex.

The simple actuators they are using may work ok for their minimal thrust steam tests so far, but it will be far from simple on the upper stage, which needs much higher performance and is peroxide/kerosene. Actual combustion chambers will need to be involved.

Differential throttling always sounds great on paper but is so much harder in real life. Which is why it has always been abandoned. (or the rockets that tried it never succeeded)

[whitelancer64]

There’s absolutely nothing simple about attitude control with an aerospike. What in the world gives you that impression?

Their recent engine tests were for testing this control system, but they have not gone beyond tied down tethered tests so far. Basically its four valves to the four corners of the aerospike, plus valves to the four roll control jets. ARCA believe its a simpler system and have said its the reason why they are using an aerospike on the second stage. From watching their videos, it does look less complex since you don't need a gimbal that can take the thrust of the engine, high force actuators and propellant lines that need to flex.

The simple actuators they are using may work ok for their minimal thrust steam tests so far, but it will be far from simple on the upper stage, which needs much higher performance and is peroxide/kerosene. Actual combustion chambers will need to be involved.

Differential throttling always sounds great on paper but is so much harder in real life. Which is why it has always been abandoned. (or the rockets that tried it never succeeded)

The Surveyor lunar landers used differential thrust for pitch and yaw control. The N-1 also did so with the first stage engines. Dragon 2 would have used differential throttling for control during powered landings, and may still be doing so in a launch abort scenario, but there hasn't been any official statement to that effect as far as I know. Astra was planning on using differential throttling for control, not sure if they still are with the newest builds or not though.

[zubenelgenubi]

Moderator: What was true in September is still true in November.

A respected veteran contributor to NSF took his personal time and effort to summarize the ARCA presentation.  Discussion of the plausibility, or not, is ok.  Advance caution on going further, as has happened on this forum multiple times.

Thank you.

Every time we have an ARCA thread it devolves into a bunch of name calling and repetitive sniping until the thread ends up getting removed.  If you don't like ARCA, fine.  Say it once and move on.  Go read some other threads.  This repetitive griping is going to be deleted.

[gmbnz]

There’s absolutely nothing simple about attitude control with an aerospike.

I totally agree that the overall concept is... how to phrase it nicely... very left-field... and I don't think it will ever fly - however I think the thrust vectoring via differential throttling is not the most unlikely part of it.

For normal engines with turbomachinery the throttle rate is very limited, however for a glorified bottle rocket all you need to do is open and close a valve.
The Saturn V had an attitude control frequency of ~25Hz, and while a smaller rocket may need that to be a bit higher it would be very feasible to make a valve capable of adjusting flow by a decent percent at that frequency. Of course depending on the plumbing there'd be a bit of a phase delay but certainly for demo launches with low Q it seems feasible enough.

Not that ARCA have demonstrated any GNC prowess, but I guess my point is of all the implausible things in the presentation differential throttling is way down the list for me .

The Surveyor lunar landers used differential thrust for pitch and yaw control.
<snip>
Astra was planning on using differential throttling for control, not sure if they still are with the newest builds or not though.

That's neat, I didn't know that. I believe Astra gave up on that but I'm struggling to find a source for that info other than memory!

[JCRM]

They could make the first stage a bit smaller if they just used decomposed HTP. That seems to be a lot less complex, and gets higher Isp, about 117 seconds.

That's what they *were* doing, before they switched to hot water. Problems getting/storing supplies of HTP? was the reason, if my atrocious memory serves.

[gin455res]

Usually when people post the results of modelling high altitude launch sites, the performance benefits turn out to be marginal. However, conventional isp rockets accelerate slowly and hit mach 1 ish at 10ish km. ARCA is aiming to get to mach 2.5 at 8.5km.


Has anyone  modelled the performance gains mountain/high-plateau (>2500m alt) launch would give an ARCA-like system?

[Steven Pietrobon]

First stage lifted into test stand. First launch of Ecorocket in June 2021 carrying two satellites.

[JCRM]

Episode 1?

Started again. *sigh*

[xyv]

Well hey the aerospike is green now.  6 months?  For an orbital attempt with an engine that leaked before the test last time and still didn't go boom!  Doesn't even feel like they're trying anymore (to pretend that they're serious that is).

[Steven Pietrobon]

For an orbital attempt with an engine that leaked before the test last time and still didn't go boom!

The engine did not leak as far as I know. It was the composite propellant tank that leaked. This was replaced with a spherical tank which looks to have been successfully tested with the engine.

[jamesh9000]

Any word on the December 9 first stage test? Obviously it hasn't happened yet, but is it still supposed to?

[Steven Pietrobon]

Any word on the December 9 first stage test? Obviously it hasn't happened yet, but is it still supposed to?

That hasn't been performed yet, as far as I know. They've only managed to load the first stage into the test stand.  I would imagine this test is still being planned, but I don't know for sure.

Here are a couple of grabs of the test with the spherical tank. A final situation report on this test is planned to be shown.